1. Field of the Invention
This invention relates to a method and intermediates useful in the preparation of N,N'-dimethyl aromatic diamines, to such compounds, and to their use as epoxy curatives, and in other applications.
2. Description of the Prior Art
Polyamines react with epoxide prepolymers to cure them by a polyaddition reaction to form tough, resinous compositions having utility as encapsulants for electronic components, adhesives, coatings, and the like. When filled, and reinforced, e.g., with glass or graphite fibers such compositions, especially those made from aromatic polyamines and epoxy prepolymers provide structural composites useful where high strength and toughness are required, for example in aircraft.
Aromatic polyamines corresponding to the following general structure are generally known to be useful in such polyaddition reactions: ##STR1## wherein ##STR2## any alkyl or aryl divalent radical, and such radicals terminated, interrupted or interrupted and terminated by --O--, --S-- and ##STR3##
Moreover, aromatic polyamines corresponding to the general formula: ##STR4## in which R is derived from, e.g., an aliphatic diol, Ar represents, e.g., phenylene and R' represents, e.g., hydrogen or an alkyl radical, and r is, for example, 2, are described in U.K. Pat. No. 1,182,377 to be useful to form polyaddition products with epoxide compounds having more than one epoxide group per molecule. Such products are disclosed to be useful as bonding agents in the production of moldings, coatings, laminates, especially glass-filled laminates, and molding compositions. From page 3, line 117, to page 4, line 3, a distinct preference is stated for compounds wherein R' is hydrogen.
In U.S. Pat. No. 3,932,360, diamine cured polyurethane products are described, in which the diamines are of the formula, e.g., ##STR5## wherein n is an integer from 2 to 12. This patent does not describe any N-alkyl substituted diamines.
N-methyl derivatives of such amines have now been found to comprise an important family of epoxy resin curing agents. It is, therefore, desirable to provide a general method to prepare N-alkyl substituted diamines in light of their ability to provide, for example, epoxide polyaddition compositions with improved properties.